Elastic fluid turbine



Dec. 2, 1952 A. FRANKEL ELASTIC FLUID TURBINE 2 SHEETSSHEET 1 Filed 001;. 4, 1949 allllllll Dec. 2, 1952 A. FRANKEL ELASTIC FLUID TURBINE.

2 SHEETS-SHEET 2 Filed Oct. 4, 1949 Patented Dec. 2, 1952 UNITED l ENT OFFICE ELASTIC FLUID TURBINE Application October 4, 1949, Serial No. 119,499 In Great Britain October 5, 1948 9 Claims.

The invention relates to the fixing of stator blades of elastic fluid turbines such as gas turbines or of axial flow turbo-compressors.

Particularly in gas turbines the problem arises of providing an arrangement for the fixing of the stator blades in their blade retaining ring which is not adversely affected by their differential thermal expansion, and which is easy to manufacture and to assemble or to dismantle.

In the assembly comprising the stator blades and a blade retaining ring of an elastic fluid turbine or axial flow turbo-compressor according to the invention the blade retaining ring has inward projections from its uninterrupted annular portion enclosing slots between themselves, and has an annular recess, coaxial with the turbine, on one of its faces across the said projections adjacent the said uninterrupted annular portion, the roots of the stator blades being profiled to match the said slots and having lateral lugs fitting into the said annular recess, extending over part of their axial length only, the rest of the blade root being free from re-entrant portions.

This arrangement allows the machining of the surfaces of the blade retaining ring, provided for radially retaining the blade roots, by simple turning. These surfaces may be either the concave and the convex surfaces of the said annular recess, or the convex surface of the said annular recess and the tips of the said inward projections of blade retaining ring.

The slots in the blade retaining ring may be machined through in an axial or in an oblique direction for example by milling, slotting, breaching, or by any machining process known for generating the teeth of internal gearing. Accordingly, the contours of the flanks of the slots may be straight lines, broken or unbroken, converging or parallel, or they may be curves such as involutes. However, "re-entrant portions in these flanks are unnecessary and even undesirable since the aforesaid turned surfaces on the blade retaining ring are those intended for radially retaining the blade roots.

The blade roots are machined to match the flanks of the slots and to engage with their lateral lugs either both the convex and concave turned surface of the said annular recess, or alternatively to engage the convex surface of the said recess with the inner surface of their lateral lugs, and to engage the inner tips of the radial projections with the shoulders formed by the blade platforms.

The lateral lugs of the stator blade roots may be arranged right at the end of the root when the bottoms of the slots in the blade retainin ring are approximately on the same diameter with the concave surface of the annular recess in said ring. Alternatively these lugs may project from the flanks of the blade root intermediate the end of the root and the platform portion of the blade, when the said annular recess crosses the slots in the blade retaining ring.

An arrangement as set forth in patent application Ser. No. 75,334 filed February 14, 19 9 by Adolf Franke1 and Alec B. Mitchell (assignors to The English Electric Co. Ltd.) for the restriction of the cross section of the metal path available for the heat conduction from the aerofoil portion of the stator blades to the continuous portion of the blade retaining ring can be applied with advantage to the present assembly: bores parallel to the direction in which the slots are machined through the blade retaining ring and/or cut-outs intermediate the front and rear face can be provided in the blade roots and/or projections of the blade retaining ring.

The arrangement according to the invention is particularly suitable for blade retaining rings and stator blades having comparatively large axial dimension such as are used in conjunction with stator blades with platforms overhanging the tips of the adjacent rotor blades, as set forth in the aforesaid patent application Ser. No. 76,334 filed February 14, 1949 by Adolf Frankel and Alec B. Mitchell (assignors to The English Electric Co.Ltd.).

In order that the invention may be better understood and readily carried into effect, some embodiments thereof will now be described by Way of example and with reference to the accompanying drawings of which Fig. 1 is a partial front elevation of one embodiment of a blade retaining ring.

Fig. 2 is a side elevation in section on line 22 of Fig. 1.

Fig. 3 is a front elevation of part of a stator blade to match the blade retaining ring according to Figs. 1 and 2.

Fig. 4i is a side elevation of the part of the stator blade shown in Fig. 3.

Fig. 5 is a partial front elevation of another embodiment of a blade retaining ring.

Fig. 6 is a side elevation in section on line 6-6 of Fig. 5.

Fig. 7 is a front elevation of part of a stator blade to match the blade retaining ring according to Figs. 5 and 6.

Fig. 8 is a side elevation of the part of the stator blade shown in Fig. 7.

Referring new first to Figs. 1 to 4 of the accompanying drawings the blade retaining ring shown in Figs. 1 and 2 has an uninterrupted annular portion I and projections ia extending inward therefrom, enclosing trapezium-shaped slots 3 extending right through the blade retaining ring in an axial direction. An annular groove 2 is machinedin the front face of the blade retaining ring across the said projections la.

The blade shown in Figs. 3 and 4 has an aerofoil portion 4, a platform 5 the shoulders of which match the tips of the projections Ia of the blade retaining ring shown in Figs. 1 and 2, and a wedge shaped root 6 adapted to match the trapezium shaped slots 3 of. the said ring. This root is provided with lateral lugs l extending axially from the front face of the blade to the same depth as the annular groove is'cut into the front face of the blade retaining ring;

The outer surface of these lugs '7 matches'the concave surface of said groove 2, and the inner, surface thereof matches the convex surface of the saidgroove.

The wedge shaped roots 6 maybe provided near their broader base with abore 6a (Fig. 3) in order to restrict the path available to heat conduction from the aerofoil portion 4 of the blade to the blade retaining ring. Alternatively or additionally, a recess 6b may be provided (Fig. 4) in the blade root 6 betweenthe inner ends of the lugs land the back face of the blade root.

Similarly, the wedge shaped projections la of the blade retaining ring may be provided with bores 3a (Fig. 1) and/or recesses 3b (Fig. 2), in order to restrict the path available for the conduction of heat to the uninterrupted portion I of the said ring.

Possible alternatives to the trapezium shaped slots 3 and 'blade roots 6 are: rectangular slots and roots, or slots and roots having a profile delimited. by broken lines, say parallel lines near the blade-platforms and converging lines near the uninterrupted portion of the blade retaining ring.

Thefit between the blade retaining ring and theiblades retaining the latter in the radial direc tion is here provided between the outer surface of the lugs T and the concave surface of the groove ion the one hand, and the inner surface of. the lugs and the convex surface of the said groove 2- on the other hand.

Referring now to the Figs. 5 to 8 of the accompanying drawings, the flanks of the projection la are curved like those of an internal spur gear, andthe flanks of the blade roots 6' shaped to matchthe gaps 3 between these projections Ia.

The-annular recess 2 machined in the front face ofthe blade retaining ring across the said projections la has nowa concave surface the diameter of whichis slightly smaller than that of the virtual circle-on which the bottoms of the slots 3 lie. Accordingly, the lugs 1 project from the flanks of the root 6 at points intermediate the ends- 6c of the roots and the shoulders 5a of the platforms 5 of-"the blades. Clearance between the ends 60 of the blade roots and the bottom of the grooves 3 and between the outer surfaces 1a; of the lugs I and the. concave surface 2a of the annular groove 2 is here assumed, the fit for the retention of the blades inthe blade retaining ring beingprovided here between the shoulders 5a of the platforms 5 and the tips of the projections I a on. the one hand, and between the convexsurface 2b of the annular groove 2 and the inner surfaces lb of the lugs l on the other hand.

In order to facilitate the machining of these inner surf-aces 1b theymay bemade straight and tangent to the convex surface 21) of the groove 2. The tips 60 of the blade roots and the outer surfaces la of the lugs 1 may also be made straight in view of the clearance prevailing there. Otherwise the embodiment shown in the accompanying drawings corresponds fully to that shown in Figs. '1 to 4.

In both embodiments the top surface of the rear portion of the blade root 6d may be made to fit the corresponding surface, Id of the blade retaining ring, with very little, or no clearance. It has been shown for example in Figs. '6 and 8 that the bending moment BM, exercised by the gas on the aerofoil portion '4 of the blade, will then be balanced by forces F1 and F2 acting on the surfaces Bd and lb respectively. As the distance between those two forces considerably exceeds the depth of the groove 2, forces F1 and F2 will be smaller than any forces acting on the faces 2a and 2b would have to be if these surfaces alone were used for holding the bendingmoment BM. Therefore, a blade fixing incorporatingthis improvement can withstand bigger bending moments without undue deformation.

Both embodiments have the advantage that the'surfaces for the radial retention of the blades in the blade retaining ring can be machined by straightforward turning. The slots in the blade retaining ring can also be machined in a simple way, say by milling or any method known for the generating of teeth of an internal gearing. No great precision in regard to their angular location is required as is the case with bulb roots where the slottin and boring, although simple operations in themselves, must be very accurately located in order to obtain the required relative angular location of the bore and the slot.

The machining of the blade roots is also quite simple, and can be done by any of the well known methods, like broaching, form grinding etc. Flat inner surfaces lb also facilitate the machining as described with reference to the accompanying drawing.

It can be stated generally that some of the features of the two embodiments can be combined in various ways.

I wish it to be understood that I do not limit myself to the details of construction as shown, for obvious modifications will occur to those skilled in the art.

What I claim as my invention and desire to secure by Letters Patent is:

1. For an elastic fluid axial flow turbomachine an assembly comprising a blade retaining ring and stator blades, the said blade retaining ring having an annular outer portion, projections inwardly projecting from said outer portion and defining slots between themselves, and an annular groove, coaxial with the said ring, on one of its faces across the said projections, and the said stator blades having roots profiled to match the said slots, and lateral lugs on said roots extending over part of their axial length only and entering the said annular groove.

2. For an elastic fluid axial flow turbomachine an assembly comprising a blade retaining ring and stator blades, the said blade retaining ring having an annular outer portion, projections inwardly projecting from said outer portion and defining slotswith straight flanks between themselves, and an annular groove coaxial with the said ring on one of its faces across the said projections, and the said stator blades having straight profiled roots to match the said slots, and laterallugs on said roots extending over part of their axial length only and entering the said annular groove.

3. For an elastic fluid axial flow turbomachine an assembly comprising a blade retaining ring and stator blades, the said blade retainin ring having an annular outer portion, projections inwardly projecting from said outer portion and defining trapezium-shaped slots between themselves, and an annular groove coaxial with said ring on one of its faces across the said projections, and the said stator blades having trapezium profiled roots to match the said slots, and lateral lugs on said roots extending over part of their axial length only and entering the said annular groove.

4. For an elastic fiuid axial flow turbomachine an assembly comprising a blade retaining ring and stator blades, the said blade retaining ring having an annular outer portion, projections inwardly projecting from said outer portion and defining slots with unbroken fiank profile contours between themselves, and an annular groove coaxial with said ring on one of its faces across the said projections, and the said stator blades having roots with unbroken fia-nk profile contours to match the said slots, and lateral lugs on said roots extending over part of their axial length only and entering the said annular groove.

5. For an elastic fiuid axial flow turbomachine an assembly comprising a blade retaining ring and stator blades, the said blade retaining ring having an annular outer portion, projections inwardly projecting from said outer portion and between themselves defining slots with flanks each having a curved generatrix, and an annular groove coaxial with said ring, on one of its faces across the said projections, and the said stator blades having roots With flanks each having a curved generatrix to match the said slots, and lateral lugs on said roots extending over part of their axial length only and entering the said annular groove.

6. For an elastic fluid axial flow turbomachine an assembly comprising a blade retaining ring and stator blades, the said blade retaining ring having an annular outer portion, projections inwardly projecting from said outer portion and defining slots between themselves, and an annular groove having a convex surface and a concave surface coaxial with said ring on one of its faces across the said projections, and the said stator blades having roots profiled to match the said slots, and lateral lugs on said roots extending over part of their axial length only and fitting with their outer surfaces the concave surface of the said groove, and with their inner surfaces the convex surface of the said groove.

7. For an elastic fluid axial flow turloomachine an assembly comprising a blade retaining ring and stator blades, the said blade retaining ring having an annular outer portion, projections inwardly projecting from said outer portion and defining slots between themselves, and an annular groove having a convex surface and a concave surface coaxial with said ring on one of its faces across the said projections, and the said stator blades having roots profiled to match the said slots, lateral lugs on said roots extending over part of their axial length only and fitting with their inner surface the convex surface of the said groove, and the blade platform forming shoulders fitting with their outer surfaces the tips of the said projections.

8. For an elastic fiuid axial flow turboinachine an assembly comprising a blade retaining ring and stator blades, the said blade retaining ring having an annular outer portion, projections inwardly projecting from said outer portion and defining slots between themselves, and an annular groove having a convex surface and aconcave surface coaxial with said ring on one of its faces across the said projections, and the said stator blades having roots profiled to match the said slots, and lateral lugs on said roots extending over part of their axial length only and fitting with their inner surfaces the convex surface of said annular groove, the said stator blades fitting with the top of their roots the bottom of the said slots near their face averted from said lugs.

9. For an elastic fluid axial flow turbomachine an assembly comprising a blade retaining ring and stator blades, the said blade retaining ring having an annular outer portion, projections inwardly projecting from said outer portion and defining slots between themselves and an annular groove having a concave and a convex surface coaxial with said ring on one of its faces across the said projections, and the said stator blades having roots profiled to match the said slots and lateral lugs extending over part of their axial length only and with inner surfaces tangent to the convex surface of the said groove.

ADOLF FRANKEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 784,431 Rambal May 7, 1905 873,344 Boyce Dec. 10, 1907 1,061,754 Knape May 13, 1913 1,298,564 Rice Mar. 25, 1919 1,904,421 Doran Apr. 18, 1933 1,998,951 Downer Apr. 23, 1935 2,354,587 Franck July 25, 1944 2,392,281 Allen Jan. 1, 1946 

